How Long Does It Take For Horse Manure To Compost

If you’re a gardener with horses, or lucky enough to have a source for this “black gold,” you’re probably wondering how long does it take for horse manure to compost. The quick answer is that it can take anywhere from three months to a full year. The timeframe depends completely on how you manage the pile.

Composting horse manure is a fantastic way to recycle waste into a powerful soil amendment. It improves soil structure, adds vital nutrients, and helps your garden retain moisture. With a few simple techniques, you can speed up the process significantly and get that rich compost into your garden beds faster.

As mentioned, the range is broad. A hot, well-managed compost pile can break down horse manure in about three to six months. A passive, untended pile might take a year or more. The key factors that control the speed are nitrogen, carbon, air, and moisture.

Fresh horse manure is considered a “hot” nitrogen-rich material. To compost efficiently, it needs to be balanced with “brown” carbon-rich materials like straw, dried leaves, or wood shavings. The bedding mixed with the manure often provides some of this carbon, but you usually need to add more.

The Key Factors That Affect Composting Speed

Let’s look at the four elements you can control to make composting quick and easy.

1. The Carbon-to-Nitrogen (C:N) Ratio

Microbes need a balanced diet. Aim for a C:N ratio of about 25-30 parts carbon to 1 part nitrogen. Fresh horse manure with straw bedding is often close to this already. If the manure is mostly pure droppings, you’ll need to add a lot more browns. A simple rule is to mix in about twice the volume of dry leaves or straw to the volume of fresh manure.

2. Aeration (Oxygen)

Your compost pile needs to breathe. The beneficial bacteria that create heat and fast decomposition are aerobic—they require oxygen. Turning your pile regularly introduces fresh air and prevents the materials from becoming a smelly, compacted mess. A well-aerated pile decomposes much faster.

3. Moisture Content

The pile should be as damp as a wrung-out sponge. Too dry, and microbial activity slows to a halt. To wet, and you’ll get a smelly, anaerobic sludge. Check the moisture every time you turn the pile. Add water if it’s dry, or mix in dry browns if it’s soggy.

4. Pile Size and Insulation

A pile needs critical mass to heat up. A minimum of 3 feet high and wide is ideal. This size allows the center to retain heat and moisture. In cooler climates, insulating the pile with a layer of straw or a lid can help maintain the temperature, speeding up decomposition year-round.

Step-by-Step: The Quick Hot Composting Method

Follow these steps for the fastest results, aiming for finished compost in 3-4 months.

Gather and Mix Your Materials: Collect your fresh horse manure and bedding. Gather carbon materials like dried leaves, straw, or shredded paper. On a dry spot, create a base layer of coarse sticks or straw for airflow.
Build in Layers: Add a 6-inch layer of the manure mix. Then add a 6-inch layer of your brown carbon materials. Sprinkle with water if dry. Repeat until the pile is at least 3 feet tall.
Monitor the Temperature: The pile should heat up to 130-150°F within a few days. You can use a compost thermometer to check. This heat is crucial—it kills weed seeds and pathogens.
Turn Regularly: Once the temperature peaks and starts to drop (usually after 5-7 days), turn the pile. Move the outer material to the center. This re-heats the pile. Turn it every week or two to maintain speed.
Check for Doneness: The compost is ready when it’s dark, crumbly, and smells like earthy soil. The original materials should be unrecognizable. This can take as little as 3 months with diligent turning.

The Easy, No-Turn Cold Composting Method

If you have more time than effort, cold composting is for you. Simply pile the manure and bedding in a bin or heap and leave it. It will decompose slowly from the outside in. This method takes 9 to 12 months or longer. The downside is that it doesn’t get hot enough to reliably kill weed seeds, so you might see more weeds in your garden later.

Special Considerations for Horse Manure

Horse manure comes with a few specific points to remember for safe and effective composting.

Weed Seeds: Horses don’t digest seeds well. The hot composting method is essential if you want to kill these seeds and prevent a weed explosion in your garden.
De-worming Medications: Some chemicals used to de-worm horses can persist in manure and harm soil life. If you know the horses were recently treated, let the manure age in a dedicated pile for a longer period (6-12 months) before using it in food gardens.
Bedding Material: The type of bedding matters. Straw and pine shavings compost well. Sawdust from hardwoods is fine but is a very dense carbon source and requires more nitrogen and frequent turning to break down.

How to Use Your Finished Horse Manure Compost

Once your compost is dark and rich, it’s ready to work its magic. Here are the best ways to use it:

Soil Amendment: Mix 2-4 inches of compost into new garden beds before planting.
Top Dressing: Spread a 1/2-inch layer around established plants, trees, and shrubs each season. Gently rake it into the top layer of soil.
Potting Mix: Sieve the compost and mix it with coir or peat and perlite to create a nutrient-rich potting mix for containers.
Mulch: A thicker layer (2-3 inches) can be used as a moisture-retaining mulch on garden beds.

Frequently Asked Questions (FAQ)

Can you use fresh horse manure directly in the garden?

It’s not recommended. Fresh manure is too “hot” in nitrogen and can burn plant roots. It can also contain pathogens. Composting it first is safer and better for your plants.

What makes horse manure compost faster?

Shredding the materials, maintaining the right moisture, ensuring a good C:N balance, and turning the pile frequently are the best ways to accelerate composting. Smaller particle size gives microbes more surface area to work on.

Why is my horse manure compost pile not heating up?

The most common reasons are: the pile is to small, it’s to dry, it lacks nitrogen (needs more fresh manure), or it lacks oxygen (needs turning). Check these factors to troubleshoot.

How do you know when horse manure compost is ready?

Finished compost is dark brown, has a pleasant earthy smell, and has a crumbly texture. You should not be able to identify the original straw or manure pieces. A simple test is to bag a small sample for a week; if it smells bad, it needs more time.

Is composted horse manure good for all plants?

Yes, fully composted horse manure is a excellent all-purpose fertilizer and soil conditioner. It’s gentle and beneficial for vegetables, flowers, lawns, and trees.

Troubleshooting Common Problems

Smelly Pile: A rotten odor means the pile is to wet and/or lacks air. Turn it immediately to aerate and mix in dry brown materials like straw or leaves.
Pile is Damp but Cold: This usually indicates a lack of nitrogen. Add a layer of fresh horse manure or another green like grass clippings to kickstart the heating process again.
Pile is Dry and Inactive: Thoroughly soak the pile with water while turning it. Moisture is essential for microbial life, so keep it consistently damp.
Attracting Flies: Bury fresh food scraps deep in the center of the pile and always cover fresh manure additions with a layer of browns. A well-managed hot pile won’t attract many pests.

Composting horse manure is a simple, rewarding process that closes the loop on your farm or garden. By managing the basic ingredients of air, water, greens, and browns, you can produce a valuable soil amendment in just a few months. Remember, even if you just pile it and wait, nature will eventually do the work for you. But with a little active management, you’ll have rich, crumbly compost ready to feed your garden much sooner. Start your pile today, and you’ll be amazed at the results.